Exhaust tuning system for two-stroke engines

ABSTRACT

A two-stroke multiple cylinder engine includes a pair of exhaust chambers having a common control wall and each of which is connected between a corresponding plurality of selected cylinders and a common exhaust passageway. The connection between each of the chambers and the passageway is defined by a tuning section which is constructed of a sufficient length and configuration to generate a negative pressure pulse to aid scavenging and reflected positive pulses from the fired cylinder. In addition, the next fired cylinder of each group establishes super-charging of the engine. The common wall between the two tuned passageways is provided with a transfer port for transferring of a positive pressure signal from the one passageway into the opposite passageway which travels back toward the engine to provide a further positive super-charging pulse to the opposite exhaust chamber. The feedback pressure wave can be applied with particular advantage to four and two cylinder engines.

[ June 4, 1974 EXHAUST TUNING SYSTEM FOR TWQ-STROKE ENGINES Inventors: Raymond R. Reid; Richard A.

Lanpheer, both of Oshkosh, Wis.

Brunswick Corporation, Chicago, 111.

Filed: Aug. 7, 1972 .Appl. No.: 270,239

[73] Assignee:

U.S. Cl. 60/314, 123/65 E Int. Cl. F0lr 7/08, B63h 21/26 Field of Search 60/313, 314; 123/65 E References Cited UNITED STATES PATENTS 2/1970 Johnson 123/65 E 3,520,270 7/1970 Miller 60/314 UX 3,692,006 9/1972 Miller et a1 123/65 E FOREIGN PATENTS OR APPLICATIONS 886,556 10/1943 France 60/314 OTHER PUBLICATIONS Zehnder, 0., Pulse Converters on Two-Stroke Diesel Engines, Brown Boveri Review, 1968, pp. 2-6.

Primary ExaminerCarlton R. Croyle Assistant Examiner-Robert E. Garrett Attorney, Agent, or FirmAndrus, Sceales, Starke &

Sawall 57' ABSTRACT A two-stroke multiple cylinder engine includes a pair of exhaust chambers having a common control wall and each of which is connected between a corresponding plurality of selected cylinders and a common exhaust passageway. The connection between each of the chambers and the passageway is defined by a tuning section which is constructed of a sufficientlength and configuration to generate a negative pressure .pulse to aid scavenging and reflected positive pulses from the fired cylinder. In addition, the next fired cylinder of each group establishes super-charging of the engine. The common wall between the two tuned passageways is provided with a transfer port for transferring of a positive pressure signal from the one passageway into the opposite passageway which travels back toward the engine to provide a further positive supercharging pulse to the opposite exhaust chamber. The feedback pressure wave can be applied with particular advantage to four and two cylinder engines.

8 Claims, 2 Drawing Figures EXHAUST TUNING SYSTEM FOR TWO-STROKE ENGINES BACKGROUND OF THE INVENTION This invention relates to cross-charged, two-stroke engines having tuned exhaust systems.

In two-stroke engines, the fuel charge may be introduced into the cylinder through inlet ports in the cylinder side wall, with the combusted charge discharged through exhaust ports in the opposite side of the cylinder. The ports are opened and closed by the piston. The two-stroke engine has a relatively short period in which to introduce the new fuel charge. As a result, efficient removal or scavanging of the combusted gases and introduction of the new charge is required, particularly for high speed engines such as employed in outboard motors and the like.

In two-stroke engines particularly for outboard motors and the like, exhaust tuning to improve the fuel scavenging and charging has recently been a fast developing technology. Tuned exhaust systems generally produce a negative pressure pulse at the exhaust port to aid in the scavenging of the burnt fuel mixture from the cylinder.

A highly satisfactory exhaust tuning system is clearly disclosed in the copending application of Richard A. Lanpheer which was filed on Aug. 27, 1971, with Ser. No. 175,651 and which is assigned to the same assignee as this application.

In the latter system, the positive pressure pulse from the exhaust of another fired cylinder in combination with a reflected positive pressure pulse from the exhaust of the cylinder being scavenged provides for super-charging of the cylinders in a six-cylinder outboard internal-combustion engine. Thus, the positive reflected positive pressure pulse is timed to raise the pressure at the exhaust ports at just the right moment to terminate the scavenging and positively force the fuel air mixture back into the cylinder to produce supercharging. The super-charging thus prevents the possibility of over-scavenging wherein part of the fresh fuel air mixture is pulled from the cylinder and passed out with the exhaust and further increases the total charge within the cylinder. Various other systems have also been suggested in the art. For example, a pair of exhaust tubes terminating in a closed megaphone construction have been suggested to cause the pressure wave from one channel to move backwardly into the opposite channel, as a result of carefully shaped passageways within the exhaust system.

The present tuned exhaust systems have provided significant increases in the horsepower of the engine.

SUMMARY OF THE PRESENT INVENTION The present invention is particularly directed to a multiple cylinder engine with an improved tuned exhaust system providing super-charging of the engine and of particularly the individual cylinders over a rela tively wide operating range.

In accordance with the present invention, the cylinders are divided into equal banks of alternate firing units provided with separate tuned exhaust passageways to permit the generaion of negative and positive tuned pulses. Intermediate the length of the two exhaust passageways a transfer passageway means is provided and transmits the positive pressure pulse from an exhausting cylinder or cylinders to the opposite channel and thereby creates a further positive pressure pulse at the appropriate cylinder in the opposite bank. The individual tuned exhaust passageways may have a common dividing wall means with the transfer passageway defined by an appropriately located opening within the length of the wall means. Thus, the exhaust passageways function as wave guide members for the pressure pulses and permit the selection of a positive pressure signal at an appropriate point along the length thereof such that it will be transmitted into and back through the opposite exhaust passageway after an appropriate time to effect further desired super-charging phenomena, by effectively forcing the fresh fuel mixture back into the exhausting cylinder and particularly through the exhaust ports so as to super-charge the cylinder. This system can be employed with the sixcylinder system such as shown in the previously referred to application but can also advantageously be applied to any other form of two-stroke engine including two and four cylinder engines wherein the cylinders can be divided into appropriate banks with an opening provided in an appropriate position to provide a predetermined or the necessary predetermined time delay or path for the pressure wave movement.

This provides a very simple and effective means for transmitting of the positive tuning pulse from one channel to the other without the necessityfor forming carefully shaped passageways and the like.

The present invention thus provides a simple and inexpensive construction for significantly improving the construction of a two-cycle internal-combustion engine particularly for outboard motors and the like.

BRIEF DESCRIPTION OF THE DRAWING The drawings furnished herewith illustrate a preferred construction of the present invention in which the above advantages and features are clearly disclosed as well as others which will be readily understood from the following description of the illustrated embodiment.

In the drawings:

FIG. 1 is an elevational view, partly in section, of a six-cylinder outboard motor employing a six-cylinder engine utilizing a tuned exhaust system constructed in accordance with the present invention; and

FIG. 2 is a similar elevational view of an outboard motor employing a four-cylinder engine similarly constructed.

DESCRIPTION OF THE ILLUSTRATED EMBODIMENT Referring to the drawing and particularly to FIG. 1, an outboard motor 1 is illustrated including a twostroke, six-cylinder engine 2 supported upon the upper end of a drive shaft housing 3, with a tuned exhaust system generally in accordance with the teaching of the previously referred to application and further revised to incorporate the additional teaching of the present invention. Thus, the outboard motor 1 includes an exhaust extension plate 4 interposed between the lower end of the engine and an upper drive shaft housing plate 5 on the upper end of the drive shaft housing 3, with suitable interconnecting studs extending downwardly from the engine 2 with appropriate openings in the members rigidly interconnecting the assembly. Further as disclosed in the referred to application, the extension 4 can be separately interconnected to the engine through many suitable bolt means or the like to fix the exhaust extension plate to the engine.

The illustrated engine is a six-cylinder employing six horizontally disposed cylinders 6 in a vertical in-line arrangement and forming a cylinder block. Each of the six cylinders is provided with a corresponding plurality of three exhaust ports 8 also disposed in vertical alignment with each other. The engine block 7 is formed with a common exhaust cavity to the one side of the several cylinders 6 and particularly to that side including the exhaust ports 8. A water jacket cover 9 is bolted or otherwise secured to the sidewall of block 7 with appropriate openings aligned with the exhaust ports to define an exhaust chamber. The water jacket 9 includes an outwardly projecting dividing wall or ridge 10 which extends into the exhaust cavity in the cylinder block of the engine. The ridge MB is configured as a serpentine element to loop about the alternate grouped exhaust passageways 8 for the several cylinders and thereby locate the adjacent groups to the opposite sides of the ridge and define a pair of exhaust passageways. An outer exhaust manifold baffle plate 11 is secured in overlying relationship to the water jacket cover MB and includes an internal ridge or mating surface aligned with the ridge l such that in the assembled relation two distinct separate and common exhaust-passageways 12 and B3 are provided to the opposite sides of the ridgellf The one common exhaust chamber l2 communicates with the related exhaust ports 8 of the first, third and fifth cylinders 6 while the oppositely located common exhaust chamber l3 communicates with the exhaust ports 8 of the second, fourth and sixth cylinders 6 as a result of the serpentine construction of the ridge.

The exhaust chambers 12 and T3 are connected to I separate tuned exhaust passageways M and 15 extending downwardly from the engine 2 and in the illustrated embodiment, through a common exhaust tube 16 in the lower unit. The exhaust tube 16 is supported within the lower drive shaft housing 3 to define a common transfer passageway of the exhaust gases from the respective exhaust passageways M and i downwardly and outwardly through an annular passage in the propeller unit within the water.

The passageways l4 and which interconnect the exhaust chambers 12 and 13 to the common unit are especially constructed with diverging walls in the exhaust extension plate 4 and housing 3 to produce proper tuning of the individual channels for establishing negative and positive pressure signals. Thus, the passageway 15 as shown in FIG. I has slightly diverging walls permitting the expansion of the exhaust gases and development of a negative pressure pulse. The passageway M is similarly formed in the opposite plane. The passageway 15 associated with the second, fourth and sixth described cylinders in the illustrated embodiment of the invention extends downwardly slightly beyond the lowermost end of the first exhaust megaphone or passageway 34 such that its distance with respect to the exhaust passageways corresponds to that of the first system. Thus, each system will operate independently of the other and essentially in a similar manner. Further in addition to the negative pulses, a positive pulse charging is obtained as a result of reflection of a positive wave from the end of the passageways l4 and 15. Further, a subsequent exhausting port establishes a positive pressure which is also impressed on the exhaust ports of a charging cylinder, as more fully disclosed in the previously referred to application. As noted therein, such a system is highly desirable and is applicable to any engine having a common multiple three cylinders so as to produce a natural pulse tuning by having the cylinders fired apart, and thereby permitting production of a positive pulse at the appropriate time in the charging of a cylinder in a given bank.

in accordance with the teaching of the present invention, the common wall 17 between the exhaust passageways M and T5 is provided with a passageway or opening 18 intermediate the length thereof and, as shown in FIG. l within the extension plate 4, properly located with respect to the cylinder banks to establish a desired transmission of a further positive pulse signal from the one exhaust channel into the opposite exhaust channel to further assist in the super-charging of a cylinder.

Thus, when the exhaust ports are opened in any given bank, they generate a positive signal which is transmitted through the exhaust system generally as a wave guide type transmission. When the pressure wave encounters the side wall opening 18, a portion of such pressure is transmitted through the opening and travels in an opposite direction in the opposite channel and thus produces a back pressure wave to the opposite bank of exhaust ports 8. By properly locating the opening 18, the timing between the respective channels l2 and 13 is selected such that the positive waves will be impressed upon the appropriate exhaust openings in synchronism with the positive pressure pulses developed by the separate channels. Thus, generally the firing order of a six-cylinder engine may be the first, fourth, fifth, second, third and sixth cylinders. Thus, in the one bank the order will be first, fifth and third, while in the other bank it would be the fourth, second and sixth. Further, for a particular cylinder the exhaust ports will open about 97 after top dead center, with the intake or transfer port opening about 18 later. Bot tom dead center is reached about 65 after the intake or transfer ports open. In turn, the intake ports will close about 63 after bottom dead center with the exhaust port 8 closing about 18 thereafter. Top dead center is again reached about 99 after the exhaust ports 8 close. Thus, when the third cylinder 6 has fired its intake or transfer port, not shown, and its exhaust ports 8 open to establish a positive output pulse in passageways 12 and 14 with the initial scavenging of the cylinder. The effect of the positive pressure pulse from this third cylinder is to super-charge the fifth cylinder until the exhaust ports thereof close. in addition, the positive pressure pulse is transmitted through the exhaust chamber 12 and the tuned converging diverging passageway 14. In travelling down the passageway, the pressure pulse passes the opening 18 and a part of the pressure signal is transmitted into the opposite channel 15 and is transmitted or flows backwardly through the opposite channel toward the opposite exhaust passageway 13 of the second, fourth and sixth cylinders. The opening is selected such that at the desired operating speed, the positive pressure pulse travels through the first channel 12 and 14 and backwardly through the second channel 15 and 13 to arrive at the exhaust port of a then charging cylinder 2 which has been completely scavenged and has a positive pressure signal for super-charging thereof.

The particular position of the opening 18 will, of course, be dependent upon the pressure wave velocity and the distance. Generally, the desired location can be readily determined through empirical processes by cating of the opening in various positions of any particular engine and operating the engine at the particular revolution or engine speed to which the system is to be tuned. The illustrated embodiment of FIG. 1 employs a common wall 17 within which the transfer means 18 is provided. The exhaust system may of course be otherwise formed. For example, completely separate and spaced passageway elements may be used with a separate interconnecting passageway pipe joining appropriately located pressure transfer taps on the elements.

It has been found that the simple provision of the transfer passageway means between the two exhaust passageways results in a very significant improvement in the horsepower output of the engine. Further, the present invention is not limited to an engine having multiples of three cylinders but can be applied to any even numbered cylinder engines which permit a division of the cylinders into a pair of banks. Thus, the invention may advantageously be applied to a fourcylinder engine where the advantage of the positive pressure pulsing as disclosed in the above patent cannot be introduced; for example, as shown in FIG. 2.

Thus, in the embodiment of PK]. 2, the first and third cylinders are interrelated and the second and the fourth cylinders are interrelated and each pair is common to one of a pair of exhaust chambers 19 and 20 interconnected to suitable tuned passageways 2i and 22 to generate the desired reflected scavenging pressure waves. The firing of the cylinders, however, will be readily recognized as such that the positive pulse generated in one cylinder of a pair will not provide a correspondingly properly timed pulse to super-charge the associated cylinder of the pair. However, the positive pulse signal which is transmitted via the tuned passageways 21 and 22 can be transmitted via a small opening 23 into the opposite passageway and transmitted back to the opposed pair to provide the desired positive charging.

The present invention thus provides a very simple and improved means for tuning the exhaust passageways of internal-combustion engines and particularly those for outboard motor units and the like.

Various modes of carrying out the invention are contemplated as being within the scope of the following claims, particularly pointing out and distinctly claiming the subject matter which is regarded as the invention.

We claim:

1. An internaLcombustion engine including a plurality of even numbered cylinders having exhaust ports for discharging of the ignited and burnt charge, at least a pair of individual exhaust passageway means connected to different cylinders and constructed to transmit the compressive pressure waves of the associated cylinders, comprising a transfer passageway means between said pair of exhaust passageway means spaced inwardly of said discharge ends of said passageway means and transferring of a compressive pressure wave in one passageway means to the opposite passageway means with said transferred compressive wave being transmitted to arrive at an exhaust port prior to the closing of the exhaust port to thereby effect a super-charging of the latter cylinder.

2. The internal-combustion engine of claim 1, wherein said passageway means having a common wall with said transfer opening formed in said common wall.

3. The internal-combustion engine of claim 1, including a drive shaft housing extending from one end of said engine and said exhaust passageway means extending through said housing with a common wall, said transfer opening being located within said common wall.

4. The internal-combustion engine of claim 1, wherein said individual exhaust passageway means are constructed to effect a tuned exhaust for the corresponding cylinders and generating a negative pressure signal for scavenging of the individual cylinders.

5. The internal-combustion engine of claim 3, wherein the engine includes at least two sets of three cylinders with each set of three cylinders having the cylinders connected to the crankcase 120 apart, each of said exhaust passageway means including means to produce a negative pulse at the exhaust port of each of said cylinders due to the exhaust from the corresponding fired cylinder to aid the scavenging of the fired cylinder and further establishing a subsequent positive pulse due to the firing of the next of said cylinders to be supplied to said exhaust port of the first fired cylinder in conjunction with a correspondingly timed positive pulse produced by the pressure wave from the exhaust gases of the first fired cylinder passing beyond said negative pulse producing means to produce supercharging of the fired cylinder.

6. The internal-combustion engine of claim 1, wherein said multiple cylinder engine includes at least four cylinders connected apart to a crankshaft to form two pairs of cylinders connected apart, each of said pairs of cylinders being connected to one of said individual exhaust passageway means, each of said exhaust passageway means including a negative pulse producing means to produce a negative scavenging pulse at the exhaust port of a fired cylinder as the result of the exhaust from the fired cylinder to aid in the scavenging of the fired cylinder and subsequently a positive pulse produced by the same pressure wave of the exhaust gases of the fired cylinder as the result of passing beyond said negative pulse producing means and producing a means for super-charging of the fired cylinder in addition to the positive pulse received from the op posite passageway means.

7. The engine of claim 1, wherein said engine is secured to a drive shaft housing forming a part of an outboard motor, said drive shaft housing extending downwardly from said engine and said exhaust means extending throughout the said housing, said exhaust means being formed by interconnected cast members having an integral thin cast wall separating the two exhaust passageway means, said transfer passageway means constituting an opening in the cast wall.

8. The engine of claim 1 includes at least four in-line, vertically stacked cylinders with exhaust chambers coupling every other cylinder to each other and forming the upper end of the individual exhaust passageway means. 

1. An internal-combustion engine including a plurality of even numbered cylinders having exhaust ports for discharging of the ignited and burnt charge, at least a pair of individual exhaust passageway means connected to different cylinders and constructed to transmit the compressive pressure waves of the associated cylinders, comprising a transfer passageway means between said pair of exhaust passageway means spaced inwardly of said discharge ends of said passageway means and transferring of a compressive pressure wave in one passageway means to the opposite passageway means with said transferred compressive wave being transmitted to arrive at an exhaust port prior to the closing of the exhaust port to thereby effect a super-charging of the latter cylinder.
 2. The internal-combustion engine of claim 1, wherein said passageway means having a common wall with said transfer opening formed in said common wall.
 3. The internal-combustion engine of claim 1, including a drive shaft housing extending from one end of said engine and said exhaust passageway means extending through said housing with a common wall, said transfer opening being located within said common wall.
 4. The internal-combustion engine of claim 1, wherein said individual exhaust passageway means are constructed to effect a tuned exhaust for the corresponding cylinders and generating a negative pressure signal for scavenging of the individual cylinders.
 5. The internal-combustion engine of claim 3, wherein the engine includes at least two sets of three cylinders with each set of three cylinders having the cylinders connected to the crankcase 120* apart, each of said exhaust passageway means including means to produce a negative pulse at the exhaust port of each of said cylinders due to the exhaust from the corresponding fired cylinder to aid the scavenging of the fired cylinder and further establishing a subsequent positive pulse due to the firing of the next of said cylinders to be supplied to said exhaust port of the first fired cylinder in conjunction with a correspondingly timed positive pulse produced by the pressure wave from the exhaust gases of the first fiRed cylinder passing beyond said negative pulse producing means to produce supercharging of the fired cylinder.
 6. The internal-combustion engine of claim 1, wherein said multiple cylinder engine includes at least four cylinders connected 90* apart to a crankshaft to form two pairs of cylinders connected 180* apart, each of said pairs of cylinders being connected to one of said individual exhaust passageway means, each of said exhaust passageway means including a negative pulse producing means to produce a negative scavenging pulse at the exhaust port of a fired cylinder as the result of the exhaust from the fired cylinder to aid in the scavenging of the fired cylinder and subsequently a positive pulse produced by the same pressure wave of the exhaust gases of the fired cylinder as the result of passing beyond said negative pulse producing means and producing a means for super-charging of the fired cylinder in addition to the positive pulse received from the opposite passageway means.
 7. The engine of claim 1, wherein said engine is secured to a drive shaft housing forming a part of an outboard motor, said drive shaft housing extending downwardly from said engine and said exhaust means extending throughout the said housing, said exhaust means being formed by interconnected cast members having an integral thin cast wall separating the two exhaust passageway means, said transfer passageway means constituting an opening in the cast wall.
 8. The engine of claim 1 includes at least four in-line, vertically stacked cylinders with exhaust chambers coupling every other cylinder to each other and forming the upper end of the individual exhaust passageway means. 